As processes for bonding a ring-shaped metal component and a cylindrical metal component to each other, “ring mash bonding,” “ring projection bonding,” “edge ring projection bonding” and so on are known. FIGS. 5A-5C show explanatory views of conventional bonding processes. FIG. 5A is an explanatory view of a ring mash bonding process, FIG. 5B is an explanatory view of a ring projection bonding process, and FIG. 5C is an explanatory view of an edge ring projection bonding process (“RingMash” is a registered trademark in Japan).
A ring mash bonding process is a solid-phase bonding process in which a cylindrical metal member is press-fitted in an opening of a ring-shaped metal member and a current is applied to achieve bonding therebetween. As shown in FIG. 5A, a cylindrical metal member 11 has a cylindrical portion with a diameter that is slightly larger than the diameter of an opening 13 of a ring-shaped metal member 12. The cylindrical metal member 11 has an edge portion having a taper portion 14a, and the ring-shaped metal member 12 also has an edge portion having a taper portion 14b. After the taper portion 14a of the cylindrical metal member 11 and the taper portion 14b of the ring-shaped metal member 12 are brought into contact with each other, the cylindrical metal member 11 is press-fitted in the opening 13 of the ring-shaped metal member 12 by applying a pressure to the cylindrical metal member 11 and a current is applied between the cylindrical metal member 11 and the ring-shaped metal member 12, thereby causing the contact portions of the cylindrical metal member 11 and the ring-shaped metal member 12 to undergo plastic flow to achieve bonding therebetween.
A ring projection bonding process is a resistance welding process in which a current is applied to a projection provided on one of a cylindrical metal member and a ring-shaped metal member until the metal is melted to achieve bonding. As shown in FIG. 5B, a projection 15 is provided on one of the cylindrical metal member 11 and the ring-shaped metal member 12. FIG. 5B shows a case where a projection 15 is provided on the cylindrical metal member 11. The cylindrical metal member 11 and the ring-shaped metal member 12 are then pressed against each other and a current is applied until the projection 15 is melted to achieve bonding therebetween. The function of the projection 15 is to reduce the contact area between the metal members. This enables the current to be concentrated at the projection 15 for effective heat generation. This process is suitable for welding between metals with low resistance.
An edge ring projection bonding process is a resistance welding process in which an edge portion of one of a cylindrical metal member and a ring-shaped metal member is used as a projection and a current is applied to the projection until the metal is melted to achieve bonding between the cylindrical metal member and the ring-shaped metal member. As shown in FIG. 5C, the cylindrical portion of the cylindrical metal member 11 has a diameter that is slightly larger than the diameter of the opening 13 of the ring-shaped metal member 12, and the cylindrical metal member 11 has an edge portion having a taper portion 14. In addition, the edge portion of one of the cylindrical metal member 11 and the ring-shaped metal member 12 is used as a projection 15. FIG. 5C shows a case where the edge portion of the ring-shaped metal member 12 is used as a projection 15. The cylindrical metal member 11 and the ring-shaped metal member 12 are then pressed against each other to press-fit the cylindrical metal member 11 in the opening 13 of the ring-shaped metal member 12 and a current is applied to the projection 15 until it is melted to achieve bonding between the cylindrical metal member and the ring-shaped metal member.
In recent years, ring mash bonding is attracting attention as a process for bonding metals of drive system components of automobiles, and expected as a process that can replace electron beam welding and bolt joining from the standpoint of running cost, cycle time and the like. As described above, ring mash bonding is a press-fitting type bonding process characterized in that bonding depth can be increased in the axial direction and high coaxial accuracy can be easily achieved without the need for the use of a positioning jig compared to ring projection bonding.
As a modification of the ring mash bonding process, a process is known in which an inner peripheral wall portion of a first metal member and an outer peripheral wall portion of a second metal member are both formed with a stepped configuration so that two separate bonded portions can be created with a gap therebetween. With this process, a bonding structure that is strong against bending in particular can be constructed without the need for immoderately increasing the axial length of each bonding portion (bonding length), and the bonding strength can be effectively improved without increasing the bonding energy (refer to Patent Document 1, for example).